Removal of toxic compounds, such as heavy metals, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), pesticides and herbicides, is one of the most difficult challenges in water treatment. Removal of these toxic compounds from wastewater for proper disposal is important for ensuring adequate environmental and public health protective measures are undertaken in order to avoid costly remediation measures as a result of inadequate wastewater treatment processes.
Currently known and utilized processes and materials are limited in their ability to remove the priority pollutants. Additionally, these current solutions are costly, energy intensive, both in the filter media itself and in pumping the contaminated water through the filter media. These current solutions also take up valuable landfill space when the filtration media needs to be disposed after reaching the end of its useful life. The currently prevailing treatment technologies used in treatment of wastewater for heavy metal removal include reverse osmosis (RO), ion exchange resin, activated carbon adsorption, and chemical coagulation and flocculation. However, as will be described further herein below, each of these known technological solutions have many limitations that are addressed by the inventive subject matter disclosed herein.
It is known to use a filtration technology called reverse osmosis for water filtration, and this technology has even been adapted for use in residential water treatment systems. Reverse osmosis filtration systems use a semipermeable membrane to remove contaminants from the liquid being filtered. However, reverse osmosis cannot tolerate the presence of, and is ineffective at removing oil, grease, dissolved dirt and/or silt, and heavy organic materials (e.g., algae, phytoplankton, vegetation debris, and chlorine) from the liquid being processed. In fact, oil, grease, dissolved dirt and/or silt and heavy organic materials will block the reverse osmosis material, such that reverse osmosis would not work when sufficient concentrations of such contaminants are present in a wastewater source. Additionally, reverse osmosis has the additional disadvantage in that it generates 25 percent more in wastewater, for the water that is filtered, such that this wastewater generated must be further processed in some manner.
Another known wastewater treatment technology is ion exchange resin (IER), however this technology has the disadvantage that it also cannot tolerate and is ineffective at removing oils, grease, and organic materials. Additionally, IER must, in order to be effective, be operated at very low flow rates in order to remove the limited contaminants that it is capable of removing. As a result, IER requires a very large volume for effective processing on any sort of industrial scale and requires longer retention time of the water for effective processing. IER also has an extremely high cost associated with its implementation, is dependent on fossil fuels for the raw material for manufacturing the filtration media and has a high cost for disposal of the filtration media, with marginal ability to further process the filtration media for reuse in many applications. Additionally, IER must be regenerated (e.g., refreshed) using toxic acids and chemicals, thereby generating additional wastewater during the clean-up process. As such, the safe disposal and clean-up from an IER filtration system is itself a secondary source of environmental pollution.
Conventional Granular Activated Carbon (GAC) is the most commonly employed filter media in heavy metal removal from wastewater. While the ability of GAC to remove heavy metals has been shown to be only marginally, if at all, successful, GAC is nevertheless widely considered to be the best media for their removal. However, GAC cannot be used to remove oil or grease but is effective to remove organic and inorganic chemicals from wastewater. As is already known, GAC is typically manufactured from a source material of rice husk, coconut shells, animal bones, and/or clam shells. This source material is first pulverized and then incinerated into ash (e.g., small particles) before final treatment with toxic chemicals in order to produce the resultant GAC product. The small particle size is easily clogged by pollutants, thus making this approach unsuccessful. Due to the energy consumption and time required to produce GAC for use in a filter media, GAC is also a very costly media. Additionally, the manufacturing process used in making GAC remains expensive and the cost is actually becoming higher over time because of the inflation of raw material costs.
Chemical treatments, such as treatments using coagulants, are time consuming, expensive, imprecise, and require large volumes of equipment for the containment of the wastewater for treatment, mixing of the chemical treatment, settling of the contaminants drawn from the solution, and drying of these contaminants. Each of these chemical treatment processes also consume comparatively vast amounts of energy for pressing out excess water and drying, by heating and/or convectively evaporating the water from the removed contaminants, the contaminants removed during treatment. Furthermore, the dried “cake” of contaminants is heavy, expensive to transport for disposal, and does not easily lend itself to recovering the potentially valuable resources contained therein, which were previously contaminants in the wastewater before the treatment thereof.
Additionally, according to the known filtration solutions using reverse osmosis, GAC, and chemical treatments, such filtration techniques require hydraulic systems to force the wastewater through the treatment units. The energy consumed in overcoming the head pressure losses inherent in such systems is significant, adding to the expense associated with such treatment techniques. Regardless of the filtration technologies used, waste, whether a secondary wastewater from reverse osmosis, spent filter media from GAC or IER, or the contaminant “cake,” is generated and must be further processed or disposed of. When a filtration media is spent (e.g., sufficiently saturated with filtrate so as to no longer be an effective filter), this spent filtration media must be buried in a landfill, further adding to the expense associated therewith. Furthermore, this waste byproduct, whether spent filtration media, wastewater, or the contaminant “cake,” itself becomes a potential environmental hazard if not adequately disposed of.
As such, there exists a strong commercial, as well as environmental, need to develop improved and alternate filtration media, filtration systems, and filtration methods, having improved efficacy and lower associated costs in removing toxic contaminants from wastewater.